CD4 and graft versus host disease: Prior studies have shown that not only does the proliferation of CD8+ Tregs exceed that of CD4+ Tregs under certain conditions (16, 25), but the induced CD8+ Tregs (CD8+ iTregs) represent a larger proportion of induced Tregs (iTregs) in GVHD (26), which implies that it is easier to induce the formation of CD8+ iTregs in vitro and may help to address the insufficient source of CD4+ Tregs.